<stránka
	xmlns="https://trac.frantovo.cz/xml-web-generator/wiki/xmlns/strana"
	xmlns:m="https://trac.frantovo.cz/xml-web-generator/wiki/xmlns/makro">
	
	<nadpis>Reading files metadata using relpipe-in-filesystem</nadpis>
	<perex>accessing file metadata like path, type, size or owner</perex>
	<m:pořadí-příkladu>01200</m:pořadí-příkladu>

	<text xmlns="http://www.w3.org/1999/xhtml">
		
		<p>
			Our filesystems contain valuable information and using proper tools we can extract them.
			Using <code>relpipe-in-filesystem</code> we can gather metadata of our files and process them in relational way.
			This tools does not traverse our filesystem (remember the rule: <em>do one thing and do it well</em>),
			instead, it eats a list of file paths separated by <code>\0</code>.
			It is typically used together with the <code>find</code> command, but we can also create such list by hand using e.g. <code>printf</code> command or <code>tr \\n \\0</code>.
		</p>
		
		<m:pre jazyk="bash">find /etc/ssh/ -print0 | relpipe-in-filesystem | relpipe-out-tabular</m:pre>
		
		<p>
			In the basic scenario, it behaves like <code>ls -l</code>, just more modular and machine-readable:
		</p>
		
		<pre><![CDATA[filesystem:
 ╭───────────────────────────────────┬───────────────┬────────────────┬────────────────┬────────────────╮
 │ path                     (string) │ type (string) │ size (integer) │ owner (string) │ group (string) │
 ├───────────────────────────────────┼───────────────┼────────────────┼────────────────┼────────────────┤
 │ /etc/ssh/                         │ d             │              0 │ root           │ root           │
 │ /etc/ssh/moduli                   │ f             │         553122 │ root           │ root           │
 │ /etc/ssh/ssh_host_ecdsa_key       │ f             │            227 │ root           │ root           │
 │ /etc/ssh/sshd_config              │ f             │           3262 │ root           │ root           │
 │ /etc/ssh/ssh_host_ed25519_key.pub │ f             │             91 │ root           │ root           │
 │ /etc/ssh/ssh_host_ecdsa_key.pub   │ f             │            171 │ root           │ root           │
 │ /etc/ssh/ssh_host_rsa_key         │ f             │           1679 │ root           │ root           │
 │ /etc/ssh/ssh_config               │ f             │           1580 │ root           │ root           │
 │ /etc/ssh/ssh_host_ed25519_key     │ f             │            399 │ root           │ root           │
 │ /etc/ssh/ssh_import_id            │ f             │            338 │ root           │ root           │
 │ /etc/ssh/ssh_host_rsa_key.pub     │ f             │            391 │ root           │ root           │
 ╰───────────────────────────────────┴───────────────┴────────────────┴────────────────┴────────────────╯
Record count: 11]]></pre>

		<p>
			We can specify desired attributes and also their aliases:
		</p>
		
		<m:pre jazyk="bash"><![CDATA[find /etc/ssh/ -print0 \
	| relpipe-in-filesystem \
		--file path --as artefact \
		--file size \
		--file owner --as dear_owner \
	| relpipe-out-tabular]]></m:pre>
	
		<p>And we will get a subset with renamed attributes:</p>
	
		<pre><![CDATA[filesystem:
 ╭───────────────────────────────────┬────────────────┬─────────────────────╮
 │ artefact                 (string) │ size (integer) │ dear_owner (string) │
 ├───────────────────────────────────┼────────────────┼─────────────────────┤
 │ /etc/ssh/                         │              0 │ root                │
 │ /etc/ssh/moduli                   │         553122 │ root                │
 │ /etc/ssh/ssh_host_ecdsa_key       │            227 │ root                │
 │ /etc/ssh/sshd_config              │           3262 │ root                │
 │ /etc/ssh/ssh_host_ed25519_key.pub │             91 │ root                │
 │ /etc/ssh/ssh_host_ecdsa_key.pub   │            171 │ root                │
 │ /etc/ssh/ssh_host_rsa_key         │           1679 │ root                │
 │ /etc/ssh/ssh_config               │           1580 │ root                │
 │ /etc/ssh/ssh_host_ed25519_key     │            399 │ root                │
 │ /etc/ssh/ssh_import_id            │            338 │ root                │
 │ /etc/ssh/ssh_host_rsa_key.pub     │            391 │ root                │
 ╰───────────────────────────────────┴────────────────┴─────────────────────╯
Record count: 11]]></pre>

		<p>
			We can also choose, which path format fits our needs best:
		</p>


		<m:pre jazyk="bash"><![CDATA[find ../../etc/ssh/ -print0 \
	| relpipe-in-filesystem \
		--file path \
		--file path_absolute \
		--file path_canonical \
		--file name \
	| relpipe-out-tabular]]></m:pre>
	
		<p>The <code>path</code> attribute contains the exact same value as was on input. Other formats are derived:</p>
	
		<pre><![CDATA[filesystem:
 ╭────────────────────────────────────────┬───────────────────────────────────────────────────┬───────────────────────────────────┬──────────────────────────╮
 │ path                          (string) │ path_absolute                            (string) │ path_canonical           (string) │ name            (string) │
 ├────────────────────────────────────────┼───────────────────────────────────────────────────┼───────────────────────────────────┼──────────────────────────┤
 │ ../../etc/ssh/                         │ /home/hack/../../etc/ssh/                         │ /etc/ssh                          │                          │
 │ ../../etc/ssh/moduli                   │ /home/hack/../../etc/ssh/moduli                   │ /etc/ssh/moduli                   │ moduli                   │
 │ ../../etc/ssh/ssh_host_ecdsa_key       │ /home/hack/../../etc/ssh/ssh_host_ecdsa_key       │ /etc/ssh/ssh_host_ecdsa_key       │ ssh_host_ecdsa_key       │
 │ ../../etc/ssh/sshd_config              │ /home/hack/../../etc/ssh/sshd_config              │ /etc/ssh/sshd_config              │ sshd_config              │
 │ ../../etc/ssh/ssh_host_ed25519_key.pub │ /home/hack/../../etc/ssh/ssh_host_ed25519_key.pub │ /etc/ssh/ssh_host_ed25519_key.pub │ ssh_host_ed25519_key.pub │
 │ ../../etc/ssh/ssh_host_ecdsa_key.pub   │ /home/hack/../../etc/ssh/ssh_host_ecdsa_key.pub   │ /etc/ssh/ssh_host_ecdsa_key.pub   │ ssh_host_ecdsa_key.pub   │
 │ ../../etc/ssh/ssh_host_rsa_key         │ /home/hack/../../etc/ssh/ssh_host_rsa_key         │ /etc/ssh/ssh_host_rsa_key         │ ssh_host_rsa_key         │
 │ ../../etc/ssh/ssh_config               │ /home/hack/../../etc/ssh/ssh_config               │ /etc/ssh/ssh_config               │ ssh_config               │
 │ ../../etc/ssh/ssh_host_ed25519_key     │ /home/hack/../../etc/ssh/ssh_host_ed25519_key     │ /etc/ssh/ssh_host_ed25519_key     │ ssh_host_ed25519_key     │
 │ ../../etc/ssh/ssh_import_id            │ /home/hack/../../etc/ssh/ssh_import_id            │ /etc/ssh/ssh_import_id            │ ssh_import_id            │
 │ ../../etc/ssh/ssh_host_rsa_key.pub     │ /home/hack/../../etc/ssh/ssh_host_rsa_key.pub     │ /etc/ssh/ssh_host_rsa_key.pub     │ ssh_host_rsa_key.pub     │
 ╰────────────────────────────────────────┴───────────────────────────────────────────────────┴───────────────────────────────────┴──────────────────────────╯
Record count: 11]]></pre>

		<p>
			We can also <em>select</em> symlink targets or their types.
			If some file is missing or is inaccessible due to permissions, only <code>path</code> is printed for it.
		</p>
		
		<p>
			Tip: if we are looking for files in the current directory and want omit the „.“ we just call: <code>find -printf '%P\0'</code> instead of <code>find -print0</code>.
		</p>
		
	</text>

</stránka>